This invention relates to seals for retaining pressurized fluids within containers. More specifically, this invention relates to seals for retaining pressurized fluids within containers, the pressures on the fluid to be contained being of such a magnitude as to require both primary sealing for low pressure sealing and secondary sealing for high pressure sealing.
For as long as man has concerned himself with attempting to contain fluids in multi-piece containers he has been faced with the problem of sealing the interfaces between the container components against leakage. The sealing means which have been devised range from simple gaskets to complex pressure responsive seals.
The simple sealing devices such as O-rings and other structures traditionally have been made of materials such as rubber, elastomeric materials, graphite and the like. As is well known to those having skills in this art, such materials are deformable under high pressure and otherwise lack the molecular structure to support either the shear forces or face loadings which may be experienced.
Because of the inability of non-metallic seals to effect satisfactory containment of fluids at relatively high pressures, those skilled in these arts have resorted to seals wherein the sealing is effected by a metal-to-metal surface engagement. In static sealing situations, for example, it is known to utilize straight compression washers wherein the initial tightening load provides the elastic force against the face constituting the seal. Dynamic sealing devices, i.e. sealing structures wherein sealing force is generated by multiplying the effective sealing pressures such as by utilizing unbalanced areas, have heretofore required careful design and coordination. Ordinarily such seals utilize metal-to-metal contact and operate by causing initial alignment forces to effect an elastic-sealing engagement between seal components to establish a low-pressure seal whereafter increased pressures cause elastic deformation of the seal components so as to reinforce the seal. Typical of structures which utilize such a design are plug valves, ball valves, mushroom seats and complex multiple component seals.
Such prior art structures have been found to be disadvantageous because they are self-limiting. More specifically, by incorporating the primary and secondary sealing structures into a single functioning unit, the structure must be responsive to the relatively low primary sealing pressures thus inherently limiting the pressure handling ability of the structure in the secondary or high pressure sealing phase. In this regard, the nature of the difficulty which is experienced is that the seal structure undergoes plastic rather than elastic deformation thereby destroying the seal.